Browsing by Author "He, G"

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    Dual-ion intercalation to enable high-capacity VOPO4 cathodes for Na-ion batteries
    (Elsevier, 2021-01-01) Zhang, Z; Ni, Y; Avdeev, M; Kan, WH; He, G
    VOPO4 is a potential cathode candidate in sodium-ion batteries for multi-electron reactions to attain high capacity up to 330 mAh g−1. However, most current efforts are focused on the V5+/V4+ redox reaction with a moderate capacity of <150 mAh g−1. Here, we report for the first time the Na intercalation behaviors for both αI- and β-VOPO4 polymorph cathodes through the V5+/V4+/V3+ redox reactions. Electrochemical evaluations suggest further reduction of V4+ ions can be attained for both cathodes, as indicated by the high discharge capacities derived from a large plateau below 1.5 V vs Na/Na+ as well as various structural analyses of electrodes at different discharge states. However, only the layered αI- cathode is preferable for deep sodiation to maintain stable structure over cycling. Theoretical studies by bond-valence sum (BVS) mismatch map calculations reveal similar Na-ion migration pathways in VOPO4•2H2O and αI-NaVOPO4, but H2O molecules in the hydrate cathode have negative effect on the diffusion of Na-ions in betweenVOPO4 layers. © 2020 Elsevier Ltd. All rights reserved.
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    Lithiated Prussian blue analogues as positive electrode active materials for stable non-aqueous lithium-ion batteries
    (Springer Nature, 2022-12-16) Zhang, Z; Avdeev, M; Chen, H; Yin, W; Kan, WH; He, G
    Prussian blue analogues (PBAs) are appealing active materials for post-lithium electrochemical energy storage. However, PBAs are not generally suitable for non-aqueous Li-ion storage due to their instability upon prolonged cycling. Herein, we assess the feasibility of PBAs with various lithium content for non-aqueous Li-ion storage. We determine the crystal structure of the lithiated PBAs via neutron powder diffraction measurements and investigate the influence of water on structural stability and Li-ion migration through operando X-ray diffraction measurements and bond valence simulations. Furthermore, we demonstrate that a positive electrode containing Li2-xFeFe(CN)6⋅nH2O (0 ≤ x ≤ 2) active material coupled with a Li metal electrode and a LiPF6-containing organic-based electrolyte in coin cell configuration delivers an initial discharge capacity of 142 mAh g−1 at 19 mA g−1 and a discharge capacity retention of 80.7% after 1000 cycles at 1.9 A g−1. By replacing the lithium metal with a graphite-based negative electrode, we also report a coin cell capable of cycling for more than 370 cycles at 190 mA g−1 with a stable discharge capacity of about 105 mAh g−1 and a discharge capacity retention of 98% at 25 °C. © The Authors CC 4.0